U.S. Pat. No. 3,940,335 describes a melt filter which is combined with an extruder, in which a filter cloth is pulled from a supply reel and is supported in the extruder by a perforated plate. The pressure generated in the extruder is allowed to act on the discharged filter cloth to produce pulling forces for further transport of the filter cloth. This is achieved by cooling the discharged strip and a melt layer which adheres to it and partially remelting the melt layer. As a consequence separate filter cloth transport mechanisms are not needed. However, the filter cloth transport proceeds only very slowly and the transition from one filter cloth to another with a differently sized mesh requires stopping of the extruder and extensive assembly work.
Because of the disadvantages of the prior art, a rotatable filter plate system has been developed. Rotatable filter plates comprise recesses in a region corresponding to a melt channel. These recesses are arranged in a circle. Exchangeable perforated plates on which filter elements are situated may be inserted into the recesses. This offers, with small outlay, the possibility of rapid replacement of the filter elements and enables convenient substitution of a screen cloth of one mesh size by a screen cloth of another mesh size. When the clogged filter elements and the perforated plates which support them are removed, the filter elements must be cleaned before they are reused. This cleaning has been found to require a considerable outlay when using some cleaning processes and when cleaning is performed at high temperatures there is a danger that undesired vapors may be released.